GB2343932A

GB2343932A - Active suspension system

Info

Publication number: GB2343932A
Application number: GB0007905A
Authority: GB
Inventors: Koenraad Reybrouk
Original assignee: Monroe Auto Equipment Co
Current assignee: Tenneco Automotive Inc
Priority date: 1996-02-06
Filing date: 1997-02-04
Publication date: 2000-05-24
Anticipated expiration: 2017-02-04
Also published as: GB2343931B; GB2343932B; GB2343931A; GB0007905D0; GB0007902D0

Abstract

A piston and cylinder hydraulic actuator has a first source of damping fluid 256 providing damping fluid at a first pressure to the upper and lower portions of a working chamber 242, a second source 262,264 of damping fluid to provide damping fluid at a second pressure to the upper and lower portions of the chamber 242, and flow control means to control the position of the piston 244 in the chamber 242 comprising first and second variable restriction valves 250,252 controlling flow between the upper and lower portions of the chamber and the second source of damping fluid to the first source of damping fluid, in which the second source of damping fluid comprises first and second pumps 262,264 receiving fluid from the first source 256 and delivering it to the upper and lower portions of the working chamber respectively.

Description

2343932 ACTIVE SUSPENSION SYSTEM

BACKGROUND OF THE!NrVENTION'

1. Field of the Invention This invention relates to a suspension system for

I aut.omotive vehicles, and more particularly to an active suspension system.

2. Descrinton Of-Related Art Suspension systems are provided to filter or "isolate" the vehicle body from vertical road surface irregularities as well as to cont-rol body and -%..heel not-ion. 7n addition, suspension systems are L - also used to maintain io an average vehicle alftiL:ude to prono'Cle inproved platform stability during maneuvering. The classic passive suspension syst-en. includes a spring and a damping device in zarallel %.,-hich are located bet-ween the sprung mass (vehicle body) and the unsprung mass (wheel and axles).

Hydraulic actuators, such as shock absorbers and/or struts, are used in conjunction with conventional passive suspension systems to absorb un,..,Ianted vibration which occurs during driving. To absorb this un,,,,anted vibration, hydraulic actuators include a piston located within the pressure cylinder of the actuator i..,hich is connected to the body of the auto-nobile through a piston rod. Because the piston is able to restrict the flow of darping fluid within the working cha-4ber of the hydraulic actuator,,,hen the actuator is displaced, the actuator is 2 a'-le to produce a damping t-c--rce which counteracts the vibration of the suspension. The greater the degree to v.'-ich the flow of damning - Fluid within the...-orking chamber is restricted by the piston, the a-eater the damping forces wnich are generated by the actuator.

in recent years, substantial interest has grc-,.:n systems -,:"-i-ch can o"er n automotive vehicle susnension L;.

or and road holding over performance Tn aroved com: t.

0 of-Fered by conventional pass-;'_ve suspens-Icn. systems. 7 such imz)rovements are acnieved b%, uz-ilization c f Z i_- IL e 11 i aent susnension s y S t em". canable C electronically controlling the suspension fcrces generated by hydraulic actuators.

Different e -v e 1 S;.n ac'nievi-C: zhe --'I d ea 1 intelli cent" suspens-Ion system, called 'a full ac-__Jve s-_snensionll, are -cossible. So-metimes only _,-;-v-arric forces acting against the movement of the pistcn::.n t'mne actuator can be generated and controlled.

or slowly changing push-out forces, velocity of the piston in the actuator, can he added to tI-e dam-oing forces, called slow leveling. The most elaborate systems, full active suspensions, can generate variable forces, as well in rebound as in comnression of the actuator, regardless of- the position and rnove-ment o-f tIne niston in the actuator. it vzould be des-i-rab-le to,.nd simnly a system which comes as close as possible to t1ne Full active suspension. in addition, in the evenz that the 3 hydraulic system should fail, it would be desirable to ha-Ie the hydraulic actuator still function in a fail safe mode.

SUMMARY OF THE INVENTION

A hydraulic actuator being operable to generate damping forces comprising:

pressure cylinder; piston disposed within said pressure cylinder being operable to divide said pressure cylinder into first and second portions, said piston having first and second sides; a first source of damping fluid being operable to provide damping fluid at a first pressure to said first and second portions of said pressure cylinder; a second source of damping fluid being operable to provide damping fluid at a second pressure to said first and second portions of said pressure cylinder; a first adjustable restriction val-re being operable to at least partially control the flow of damping fluid from said first portion of said pressure cylinder and said second source of damping fluid to said first source of damping fluid; a second adjustable restriction valve being operable to at least partially control the flow of damping fluid from said second portion of said pressure cylinder and said second source of damping fluid to said first source of damping fluid, and means for controlling the pressure on each side of said piston to control the position of said piston in said pressure cylinder; wherein said second source of damping fluid comprises a first pump being operable to receiving damping fluid from said first source of damping fluid and deliver said damping fluid to said first portion of said pressure cylinder; and a second pump being operable to deliver damping L4 A-ff fluid from said first source of damping fluid from said first source of damping fluid to said second portion of said pressure cylinder.

-An.aim of the present invention is to provide a hydraulic actuator which is able to be used in an active suspension system which provides for variable damping and levelling.

Another object of the present invention is to provide a hydraulic actuator in which the damping forces generated by the hydraulic actuator are substantially independent of the position and velocity of the piston within the pressure cylinder.

It is a further object of the present invention to 15 provide a hydraulic actuator which can be used in an active-suspension system. In this regard, it is a further object of the present invention to provide a hydraulic actuator which can be used with a relatively low pressure hydraulic system. 5 Another object of 'C-he invention is to provide a hydraulic actuator which enables a fail-safe suspension design in case of massive hydraulic pressure losses. Another object of the invention is to provide a hydraulic actuator which is relatively simple and relatively inexpensive.

BRIEF DESCRIPTION OF THE DRAWINGS

Various advantages of the present invention will become apparent to one skilled in the art- upon reading the following specification and by reference to the following drawings in which:

FIG. 1 is a diagrammatic illustration of the hydraulic actuator according to the teachings of the preferred embodiment of the present invention shown in operative association with a conventional automobile; (0 FIG. 2 is a diaqraT-=atic illustration of the hydraulic actuato.r according to a f irst preferred embodiment of the present invention shown in FIG. 1; FIG. 3 is a diagrarmatic illustration of the hydraulic actuator shown in FIG. 2 using a clutch to control the mressure within %the accumulator; and FIG. 4 is a diagrammatic illustration of the hydraulic actuator shown in FIG. 2 using two switchable valves for controlling %the pressure within ', --he accumula-'Z-or- io DESCRIPTIO'l OF TFE PREFERRED E4BODIM71177S

Referring to FIG. 1, a plurality of hydraulic actuators 10 in accordance with the teachings of the nre'Eerred embodir.ent of the present invention is shown. The hydraulic actuators 10 are depicted in operative association with a conventional autonobile 12 having a vehicle body 14. The automobile 12 includes a rear susnension 16 having a transversely extending rear axle assembly 18 adapted to support the rear vheels 20. The rear axle assembly 18 is operably connected to the auto-nobile 12 by means of a pair of hydraulic actuators 10 as well as by helical coil springs 22. Similarly, the automobile 12 has a front suspension systen 24 including a transversely extending front axle assembly 26 adapted to support the front;-7hee'-s 28. The front axle assembly 26 is connected to the au'Comobile 12 by neans of a second pair of hydraulic actuators 10 and by a second pair of helical coil springs 30. While the automobile 12 has been depicted as a passenger car, the hydraulic actuators io nay be used with other types of notor vehicles as well. Furtkhermzore, the structural association of the front and rear axle assemblies are exenplary in nature and are not intended to limit-, the scope of the present invention.

To allow the forces generated by the hydraulic actuators 10 to be controlled, a node select switch 32 and an elecCronic control module 34 are prcvided. The riode -1- ch 32 is located within the select swi%_ k.. passenger compartrent 36 of the automobile 12 and is accessible by t',e occupants of the autonobile 12. The r.ode select s-.d'k--ch 32 is used for selecting the darning characteristics which 4 1- e hydraulic actuators 10 are to provide as well as to -'5 ad"1-:us4-- leveling. It will be appreciated, however, that the j % %_ switch 32 is ontional.

mode select The electr9nic control rodule 34 receives cutnut from the rode select. switch 32 as well as various sensors which are used for generating control signals for selectively controlling the forces generated by the hydraulic actuators 10. In fluid comnunication with each of the hydraulic actuators 10 is a closed-loop high pressure hydraulic system 38 which includes two pumps 262, 264 and an accumulator 256 shown in 'F'igy. 2 and more fully discussed below.

The first preferred embodiment of the present invention will now be described with reference to FIG. 2. The hydraulic actuator 210 shown in FIG. 2 comprises an elongated pressure cylinder 240 which defines a fluid containing work chamber 242. Disposed within the working chamber 242 is a reciprocal piston 244 which is operable to divide the working chamber 242 into an upper portion as well as a lower portion. The reciprocal piston 244 is secured at one end to an axial extending m; s'%on " rod 246 which is able to JT-.=)ar rovenent to miston 244.

To provide a first source of danp4ng fluid to the upper and lower portions of the working charber 242, the hydraulic actuator 210 further includes an accumulator 256.

The accU-1ulator 256 is used to store damping fluid which may. be delivered to the upper and lower portions of the :--rj,:in-- cha-,ber 242. in this regard, the accumiulato_- 256 fluidly co---Iunicates wit-h the upper port-ion of the worzing 2.0 ch a -.-b e r 242 through a first variable restriction valve 250, while the accumulator 256 fluidly commun-Lcates with the lower mor"E.-ion of the working c.-.amber 242 1--hroualn a second raria-le restriction valve 252.

k.. t.. - The "i-s and second variable restricticns valves 250 and 252 ray bebi- direct%_ional valves having a con trol!able blc-...,-of-.'L' p-ressu--re.

.:cwever, other sui-able valves may be used.

To provide a second source of damning fluid to and second portions of %the T,,,orking chamber. 21.2, the hydraulic actuator 210 further includes a first purp 262 and a second punp 264. The first punp 262 is able to receive fluid from the accumulalZor 256 and deliver the fluid to the upper portion of the working charber 242. in a similar fashion, the second pump 264 is able to receive darping fluid from "he accurmulat-or 256 and deliver the damping fluid to the lower portion of the -,:cr':-ina c"I'larber 242. The firs,'_- and second purps 262 and 264 are driven by the -Cj,_s4- a'; a riotor 260 at- a constant- smeed so that second pumps 262 and 264 provide a relatively unifor-m flow of damping fluid '%to the upper and lower portions of the working chamber 242.

The omeralE.-ion of the hydraulic actuator 210 sho-.-n in FIG. 2 will now he described. 1.7hen the hydraulic actuat-or 210 is at a static position, the first and second variable restriction valves 250 and 252 are onen therefore causing damping fluid f1cw-ing from the output of the fi_rst zump 262 to flow back to the first, pump 262 t-hrou-h the 2.0 first variable restriction valve 250. in a similar fLashion, fluid delivered by the output of the second purp 264 is delivered back to the second pump 264 through the second variable restriction valve 252. When i4C. is desired to increase the pressure of damping fluid in the upper portion of the working char-her 242, the position of the -first variable restriction valve 250 is varied thereby causing darning fluid received by the first pump 262 'fron "he accumulator 256 to be delivered to the upper portion of the working charber 242. At the same time, the second variable restriction valve 252 is open thereby allowing darping fluid in the lower portion of the working chamber 242, as well as the damping fluid flowing through,%--he second pump 264, to be delivered to the accumulator 256 as well as to the second pump 264.

V,-hen it is desired to increase the nressi,.re of damping fluid in the lower portion of the working cha--,--er 242, the first variable restriction valve 250 is cpened ;-Iile 'Che second variable restriction valve 252 is closed.

This causes the a-mounl: of damping fluid delivered by the 5=---On,d pump 264 to the lower portion of the working chamber 2'12 to increase while atthe sa-me time allowing danping fluid from 'Che u-pPer por-'Cion oLc' the working char-ber 242 to be delivered to the accu-mulator 256 by the fffirst variable restriction valve 250. Accordingly, the pressure of ing "luid in the lower por-ion of the wor' ing cha=her 242 is able to increase while t-he pressure cfL 'Che da-mping io in the upper portion of the working chamber 242 is reduced.

The hydraulic actuator 210 shown in F7G. 2 can be 7-o,_4 if ied to pro v ide me an s f o r con",, roll in g independen'Cly the static Dressure of the damping fluid within -L.--- actuator. Cne such -modification is shown in 7TG 3 in which components similar to the componenlC_-s sho-..:n in FIG. 2 are similarly labeled with the reference nu-erals incremented b-,/ 100. in addition to %the commonents described above with respect to the e7_bodi7.-,ent shown in FIG. 2 $the hydraulic actuator 310 shown in FIG. 3 further includes a reservoir 366. The reservoir 366 provides a source of damping fluid which is able to be delivered to -%he accumulator.356 so as to increase the pressure of the damping fluid in the accumulator 356. To provide means for cont-rolling the flow of darming fluid fro-m 'he reservoir 366 to the accumulator 356, the h,;'traulic actuator 310 furt%her includ-es a third pump 3608 as well as a bypass valve 370. The t-hird pump 36^0 - is on=rable to receive da-ping fluid from 'he reservoir 366 and deliver a pressurized flow of damping fluid to the accumula"Cor 356." The flow of damping fluid tothe accummulal_:or 356 is reaulated by 'he bypass valve 370 which is disposed in parallel with respect to the third pump 363 bet-ween the accumulator 356 and the reservoir 366.

V"hen the bypass valve 370 is closed, damping fluid is delivered c - i the reservoir 366 to 1-he accumula"Cor 356 through the third pump 368. V,'hen the bypass valve 370 is open, da=ping fluid is able to flow io fron the cut-pu'C_ of the 'Chird nump 368 to the innut of the thi t rd pump 368. Accordingly, the bypass valve 370 is able o control the delivery of fluid to and from- the accumulator 356 and therefore the pressure within the accumulator 356. The third pump 368 is driven by the mot%or 2.5 360 'through a controllable clutch 372. The controllable clutch 372 is used to control the speed of 'Che third pump 363 and therefore the flow of damping fluid delivered by "he third pump 368.

The hydraulic actuator 310 shown in FIG. 3 can be modified to be driven fron, a mot-or directly wilChout the need for a controllable clutch in the manner shown in F7-. 4 In this regard, the components in FIG. 4 which are similar to that shown in FIG. 3 are indicated by sinilar reference numerals which are increnented by 100. As sho'..."n, the hydraulic actual'or 410 further includes a first. swil-_-chable valve 474 and a second switchable valve 476.

L -rols the flow of daniping The -"irs"- swi-chable valve 474 conl IL fluid from -he output of the third purnp 468 to t1,,,.e J. - L - k.. t- kaccumulator 456, 'while the second switchable, valve 476 controls the flow fron the output of the third pu-,,,p 4068 to the inout of the third cur.= 468.

When the nressure of danning fluid inside the accumulator 456 is to remain static, the first swi'C-chable valve 474 is closed while the second switcl,-,,able valve 476 is open. This allows danping 'Eluid from t-he o,.;tput of the Z, - - L %, third pu-P 463 to be delivered to the input o'E the third io mumn 468. ',,7"hen it is desired to increase 'Che Dressure of switchable valve 474 is onened while the second s-.,-itc-nable valve 476 is closed thereby causing darpincr fluid fror, the outzut of the third purp 468 to be delivered to the i5 a_-cu-4ula6_o_- 456. This causes the pressure withih the accumulator 456 %to increase. 1.7hen it is desired %to reduce the pressure within the accumulator 456, the s,.:_itchable valve 474 is opened together with %the second switchable, valve 476, 'Chereby causing damping fluid in the accumulator 456 to flow into the reservoir 466. Because t-he first and second swit-chable valves 474 and 476 are operable to regulate the flow of dariping fluid into and out OIL the accumulator 456, the third punp 468 may be driven at a constant speed by t-he not-or 460 thereby eli-,ninat-ing the need for a controllable clu4Cc1,,.

As evidenced fron, the foregoing, thcse skilled in 'Che art will anoreciat-e. that the zresent- invention is a!-le actuator which is able to be used in to provide a hydraulic a suspension systen 1--o provide both variable damping and leveling. In addition, the hydraulic actuator is able to provide damping forces which are subs tantially independent from the position of %the piston wit-hin the pressure cylinder. The hydraulic actuator allows a conventional smring to be nounted in parallel with the actuator without appreciable loss of per-for7mance of the suspension s,stem. Since conventional springs nay be used, only dynanic forces io have to he cenerated by the pump thereby permit..ting cniv relatively low pressures to be used within the hydraulic s y s t- em. This perm.its relatively st-andard commonen"L.-'s to be used in the piston valve and other conzcnent-s of the -Iydraulic actuator. However, with the erabcdiments sho,..:n in FICS. 2-4 the different actuators nust- be connected to different pumps. These punps can be combined to one or two central units (keeping the hydraulic circuits separated), bu t, the pumps can also be integrated %-.-ith different actuators.

14C will also be noted that the hydraulic actuator of the present invention is operable to nininize the impact of a hydraulic systen failure. In this regard, the hydraulic actuator can be used in parallel with a spring.

in such an implenientation, the -failure of the hydraulic system, will cause the hydraulic actuaCor '%.--o work as fi=-., passive dancer.

0.

I-Th i 1 e it will he aPparent that the preferred enbodiment. illustrialted above is well calculated to fulfrill %the objects stated, it will be appreciate-,-'- that the P--esent invention is susceptible %to nodification, variation, and change without departing from the scone of" the invention. '.ccordingly, the invenlCion is %to be measured against the scone of the following clains.

CLATMS 1. A hydraulic actuator being operable to ge-n-erate damping forces comprising:

a pressure cylinder; a piston distosed within said pressure cylinder being operable to divide said pressure cylinder into first and second portions, said piston having first and second sides; a first source of damping fluid being operable to provide damping fluid at a first pressure to said first and second portions of said pressure cylinder; a second source of damning fluid being operable to provide damping fluid at a second pressure to said first and second portions of said pressure cylinder; 15 a first adjustable restriction valve being operable to at least partially control the flow of damping fluid from said first portion of said pressure cylinder and said second source of damping fluid to said first source of damping fluid; 20 a second adjustable restriction valve being operable to at least partially control the flow of damning fluid from said second portion of said pressure cvlinder and said second source of damping fluid to said first source of damping fluid, and 25 means for controlling the pressure on each side of said piston to control the position of said piston in said pressure cylinder; wherein said second source of damping fluid comprises a first pump being operable to receiving damping fluid from said first source of damping fluid and deliver said damping fluid to said first portion of said pressure cylinder; and a second pump being operable to deliver damping fluid from said first source of damping fluid from said 33 first source of damping fluid to said second portion of said pressure cylinder.

10, 2. The hydraulic actuator of claim 1, i..,herein said first source of damping fluid comprises an accu-mulator.

3. The hydraulic actuator of claim I or 2, further comprising a motor operable to drive said first and second pu-,,,.ps at a substantially constant speed.

4. The hydraulic actuator of any one of claims I to 3, further comprising means for controlling the pressure of damning fluid in said first source of damping fluid.

5. The hydraul-ic actuator of claim 4, wherein said means for controlling the pressure of damning fluid in said first source of damping fluid comprises a reservoir and means for controlling the flow of damping fluid from said reservoir to said first-source of damning fluid.

6. The hydraulic actuator of claim 5, wherein said means for controlling the flow of damping fluid from said reservoir to said first source of damning fluid includes:

(a) a third pimp operable to deliver damping fluid from said reservoir to said first source of damping fluid; and (b) a third valve being operable to control the flow of damping fluid between said second source of damping fluid and said reservoir.

7. The hydraulic actuator of claim 6, wherein said means for controlling the flow of damping fluid from said reservoir to said first source of damping fluid further includes a clutch operable to control the speed of said third pump.

47- 8. The hydraulic actuator of claim 5, further comprising:

-able to deliver damning fluid from (a a pump ope L said reservoir to said first source of damping fluid, (b) a third valve being operable to control the flow of damping fluid from said third pump to said first source of damping fluid; and (c) a fourth valve being operable to control the flow of damping fluid from said third pump to said reservoir.

9. A method for controlling the force cenerated by a hydraulic actuator having a working chamber and a piston disposed therein, said piston being operable to divide said working chamber into first and second nortions, said method comprising the steps of: delivering damping fluid from a first source of damping fluid to said first and second portions of said working chamber; 20 regulating the flow of damning fluid between said first portion of said wo-rking chamber and said first source of damping fluid by a first variable restriction valve; regulating the flow of damping fluid between said second portion of said working chamber and said first source of damping fluid by a second variable restriction valve; and controlling the pressure in said first and second portions to control the position of said piston in said working chamber.

10. The method of claim 9, wherein said step of delivering damping fluid from a first source of damping fluid to said first and second portions of said working chamber further comprises the step of allowing damping fluid in said accumulator to be delivered to a first pump, said first pump being in fluid communication with (n rl u 44 04 44 r-i 0 44 0) M r-- 04 '0 0 9 -rA 04 04 04 " (q 04 04 0) 4 U) U) rO 4J -Y, -r-i r, 04 l 0 rl q) E 4 44 10 4J -j In (li o u 0 ji (0 0 0 >1 r-A 0 U) 0 0 10: 113 Q) -ri U) ro M 41 U) A- ro '0 Ef) 4-) >1 F U) r= r. 10 (1) ,1 44 rO (Ij o 44 '0 4J 0 10 E 0 4 0 X! 10 fli 0 -,4 0) W 0.-1 0 -1 ro H ro 0.,1 _4 4-) 4J rA U) I'd rl (IS (is rl u 4-) 0 (Ij a) U) -,1 0 U) U) R5 4-4 ri > 4 ul 0: ":1 4 A 0 ro rO 4 -r-4 4 4 44 0 r a) r.,-I ro rj 0ri 4 44 J 4 r a) o r-i o f=- q rA l 0 r-l 4J.14 04 0 fo 43 > -rI r-l w 0 E 4) 0 04 j (1) E J-) r-A 4 4 41) M EA AJ 4 U (13 A U) In 04 4::$ 0 44 4 Q) (L) 0 U 4 vi Q) si 0) r4 IIJ 4-) 04 r C! (1) A lu 4) IJ 0 44 '0 0 4-J 0 fil 4-) rCJ a) Lj;I X1.

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16. A hydraulic actuator constructed and arranged substantially as hereinbefore described with reference to Figures 2 to 4 of the accompanying drawings.

17. A method substantially as hereinbefore described with reference to Figures 2 to 4 of the accompanying drawings.